If your relying on the trucks display for MPG, it's way off with a chip installed. I have yet to have anyone prove, who hand calculates MPG, that they are getting any real significant fuel savings. I'm not saying you can't but mostly people honestly tell me is it more like .5 MPG or less, nothing tremendous considering the possible damage and complications that can arise from chipping. If you can reset it with your chip programmer, can you read the codes it put out when this happened. Should pretty much tell you what heppened.

every time I Limped the tranny, I did not lock out overdrive soon enough and it limped as I was starting up a hill. Getting out of the seat and back in and starting engine about 3 times will clear the limp. I get similar MPG 23 empty and about 12 towing at about 65 mph and those are hand caculated values. The DIC is much higher. I figure the hand calc is about 5 MPG less that DIC. I use the EDGE and have a mod to the ECM.

I know you won't like this but I would get rid of the chip, your choice though, But I have a Dodge 1 ton dually 06 stock 5.9 cummins and empty get 22 around town and 12.5 tp 14 mpg towing. I tend to be like some of the others chipping usualy brings on more cost later. Just my thoughts, not being rude.
Happy Trails

Drive to work grab a second cup coffee and head to the spec and proving ground. This is the routine engineers do everyday at GM. Sometimes they don't catch items (recalls) but most of the time there on the ball. Where I'm going with this is millions are spent each model year tuning vehicles, matching transmissions to motors. They have the ok to snap crackle pop Motors & trans each & everyday. They push them to the max then back off to prevent warranty issues. These points are calibrated & set in the programs to flash to the pcm to be retained. If it was good for your $50,000 truck they would be installed from a manufacturing prospective. Cold air induction for an example, certainly would be oem by now its been an after market product for years & years an still have not made it in any autos. Its like pushing a race horse you might get away with it once, but your going to explode the poor animals heart some day...I read the forums all the time (crack crank shafts & blown trany's) & no one can say there getting better gas mileage with tuners, most get worse for they can't keep there foot out of the raging beast the tuner has turned the truck into. Really if you need a race horse, figure of speech...buy a Corvette. One awesome truck you own and I hope all works out for getting back to normality.
Blessings,